1. Field of the Invention
Embodiments of the present disclosure generally relate to a method and apparatus for controlling Silicon Controlled Rectifiers (SCRs) in an H-bridge.
2. Description of the Related Art
A common topology for DC-AC inverters employs a DC-DC booster stage followed by an H-bridge. The H-bridge acts to create a true AC waveform at the inverter output by “unfurling” a rectified sine wave received from the DC-DC booster stage. In some instances, the AC output of the DC-AC inverter may be coupled to a commercial power grid, and the H-bridge operates at the frequency of the AC line voltage on the grid. For example, distributed generators (DGs), such as solar power systems, convert DC power generated by renewable resources to AC power that may be coupled to the grid.
Many DC-AC inverters employ Silicon Controlled Rectifiers (SCRs) as the H-bridge switching elements due to their robustness, easy control, and low cost. However, in systems where the inverter output is coupled to the grid, anomalies occurring in the AC line voltage may induce a commutation failure in such an H-bridge. For example, if the AC line voltage suddenly reverses polarity prior to its normal zero-crossing, the active SCRs in the H-bridge may erroneously remain in a conductive state (“on”) during the next half of the AC line voltage cycle while the previously inactive SCRs are also switched on. This effectively “shorts” the H-bridge, resulting in an uncontrolled current surge through the inverter and subsequent damage to the inverter.
Therefore, there is a need for a method and apparatus for controlling Silicon Controlled Rectifiers (SCRs) in an H-bridge.